Superfluid helium is used, for example, during space travel for cooling of equipment. Superfluid helium is in a one phase state and there are no difficulties at the orifice of the container concerning the phase boundary liquid/gas (two phases). There is always a superfluid helium film of finite thickness at the wall of the container and so at the orifice. Only the thickness of this film is affected by the direction and magnitude of the applied force of gravity.
In known systems, such phase separators consist of plugs of a porous ceramic material or of sintered metals. Rolled, contracted foils can also be used. The mass flow then takes place through the capillaries of the plug. All of the abovementioned phase separators are passive systems in which the mass flow of helium and therefore the cooling power cannot be regulated to the required extent. An exact regulation is, however, essential when the heating losses of the equipment to be cooled vary greatly during operation.